1. Field of the Invention
This invention relates to flame-retardant compositions and more particularly relates to such compositions comprising a rubber-modified polystyrene.
2. Description of the Prior Art
It is known that normally flammable polymers can be rendered flame-retardant by the incorporation of the flame retardants of British Pat. No. 1,377,282 or the flame retardants of U.S. Pat. Nos. 3,382,204 and 3,403,036, the former being brominated monoadducts of polyhalocyclopentadienes and multi-unsaturated hydrocarbons, and the latter being diadducts of polyhalocyclopentadienes and multi-unsaturated hydrocarbons. However, neither type of flame retardant has proved to be satisfactory for incorporation into rubber-modified polystyrene compositions. The monoadducts flame-retard the compositions efficiently but lower the heat distortion and softening temperatures more than is sometimes acceptable; the diadducts, which have less deleterious an effect on heat distortion and softening temperatures, have poor efficiency as flame retardants. It would be desirable to find a flame retardant or flame retardant system capable of functioning efficiently but providing compositions having a good balance of properties.